1. Field of the Invention
The present invention relates to a method of feeding a stream of particles under pressure. Specifically, the stream may be comprised of abrasive particles which are fed to remove unwanted material from a surface. More specifically, a preferred use of the stream is the removal of undesirable material, such as decay or stains, from teeth in an air abrasion dental instrument.
2. Background of the Invention
Air abrasion instruments have been available for use by dentists for treating patients with an abrasive-laden fluid stream for many years. Among the advantages realized in air abrasion dentistry are increased patient comfort, alleviation of patient anxiety, decreased use of anesthesia, increase of dentists' productivity, and decreased costs to both patients and dentists.
This dental technique uses abrasive-laden streams which carry abrasive particles and a carrier gas. The stream is directed onto the patient's teeth for removal of decay, preparing the teeth to receive fillings, prophylactic treatment, and the like. Such air abrasion instruments provide advantages over conventional dental drills. These include eliminating the heat, noise, and vibration produced by conventional high-speed drills. Also lessened is the need for anesthesia as well as the need to cool the drill with fluid.
The use of directing a fluid stream of abrasive particles to the teeth to perform dentistry is known in the dental art. The general technique of treating teeth using such abrasive can be traced back to the 1950's and the work of Dr. Robert Black in U.S. Pat. No. 2,696,049. Some details of the feed system of Dr. Black's patent are described and presented in Comparative Figure A.
In '049, the abrasive particles were vibrated to effect their delivery from the storage compartment to the mixing chamber. The particles were kept in a constant state of motion. An improvement to the mixing system described in the Black patent was improved upon by others desiring to improve control of the flow of abrasive particles used in air abrasion dentistry.
One such improvement is recited in Ser. No. 08/975,438 filed on Nov. 21, 1997 and likewise assigned to Kreativ, Inc. This system, although equipped with such features as microprocessor and remote controls, had not greatly altered the particle feed system introduced by Dr. Black in '049. The aforementioned Kreativ patent application describes a unit which is equipped with a vibrator. The pressure in the container holding the particles varies as the dentist selects different operating pressures. The abrasive particles are gravity fed in the pending Kreativ application
Another feed system for an air abrasion dental device is described in U.S. Pat. No. 5,525,058 to Gallant et al. Gallant utilizes a closed loop regulator to control air pressure. Their system operates with a plurality of servo valves which continuously monitor the output pressure and re-adjust the pressure control if the output is too high or too low. Specific features of this technology are presented and described as Comparative Figure B.
The '058 patent employs a vibrator and does not use gravity feed, as do the systems described above by Black and in the previously mentioned pending Kreativ application. The '058 feed system operates on a pressure principle with a mixture of particles and air being forced upward under pressure with vibrational activity, against gravity, through helical means.
Another invention concerned with the delivery of abrasive powder to a hand-held dental tool for air abrasive dental treatment is taught by Abbott in U.S. Pat. No. 5,618,177. The particle feed system of '177 uses both gravity feed and oscillation in its arrangement for feeding pressurized particulate material. The '177 feeder system employs a vibrator to vibrate the bottom of a hopper where abrasive particles are stored. The vibrator applies oscillatory forces and torques to the bottom portion of the hopper causing the powder in the hopper to fluidise and circulate within the hopper and across the inlet orifice. Details of the '177 patent may be seen in Comparative Figure C.
Still another method and apparatus for an air abrasive dental unit is disclosed in U.S. Pat. No. 5,718,581 to Fernwood et al. The apparatus disclosed therein utilizes an internal vibrator motor with vibration transmitters which transmit the vibrations throughout the jar containing abrasive
In the '581 patent, the vibrator assembly in combination with the vibration transmitter maintains the favorable flow of particles under gravity feed. The particle feed system of '581 uses both gravity feed and oscillation in its arrangement for feeding pressurized particulate material. This system is illustrated in Comparative Figure D.
Prior to the instant invention, the feed systems of air abrasion dental instruments employed vibrators as part of their particle feed systems. Another feature common to the prior art systems is equalization means to equalize pressure in various parts of the unit. The particle flow of the prior art systems are not linear, have undesirable bursts of abrasive particles, and have less controllable particle feed streams.
Although linear flow is a desirable feature of air abrasion dentistry, it was not accomplished by the prior art systems. Linear particle flow, and other objects of the present invention, will be clarified shortly.